The present invention concerns packing yarns. More specifically, the present invention concerns a composite yarn having a reinforcement layer.
Packing yarns are used in the manufacture of seals, and in particular, in the packing of a stuffing box used to seal pumps and valve shafts. One conventional packing yarn is commonly formed by using an expanded film or tape using a mixture of Polytetrafluoroethylene (PTFE) and graphite and folding it into a yarn. Yarns may be formed of films, substrates, tapes, and other materials. Yarns may be expanded or not expanded, may be extruded or not extruded, and may be sintered or unsintered.
In some cases a liquid lubricant may be used to aid in the manufacturing process and/or provide increased thermal conductivity. This material exhibits good thermal and wear characteristics. One issue with this mixture is that these materials have poor tensile strength and tend to extrude easily through clearances in the stuffing box. To improve the tensile strength of the yarn, reinforcement is incorporated into the yarn. Conventional reinforced materials resist extrusion better and can handle higher pressure applications. A significant drawback of conventional materials is that they are still highly prone to extrusion and breakage during normal operation.